Several people on Twitter wrote around 2 a.m. about the nonstop foghorn.

One user wrote, "Is there some sort of 2 a.m. #foghorn concert in SF tonight? Either that or someone passed out on the horn. 20 minutes without a pause now."

Another person wrote a series of tweets around 2:20 a.m. about the unusual blasts, including, "What's with the never-ending fog horn in the SF bay right now... #rude" and "Omg. This can't be happening at 2 a.m. It can't be THAT FOGGY #foghorn #shutitdown."